INTRODUCTION
[0001] The present invention refers to a process to transesterify triglycerides of animal
or plant origin or used frying oils to obtain esters of fatty acids of low molecular
weight alcohols. Salts of carboxylic acids and alkaline metal hydroxides have been
used as a catalytic system.
[0002] The importance of this invention lies in the use of the excess acidity, presented
by all oils and fats of plant and animal origin, to obtain the catalytic system (carboxylic
acid salts), eliminating preliminary preparatory steps of the raw materials and reducing
the costs of the catalyst and the time previously required for the purification steps.
[0003] The process is carried out in moderate pressure and temperature conditions. In this
process, the reaction is carried out in continuous and discontinuous modes in a stirred-tank
reactor. The complete ester production process can be carried out in a discontinuous
or continuous mode.
[0004] In this process, the reaction is carried out with a catalytic system, partly formed
by the carboxylic acids found in free form in the raw material, permitting the preliminary
preparatory steps to be diminished and also the operation time of the process.
STATE OF THE ART OF THE TECHNIQUE
[0005] For decades, fatty acid esters have been the most important compounds in the fat
industry and in oil chemistry, because of their important role as intermediate products
in the production of other esters, amines, fatty alcohols and soaps, among others.
Excellent applications have been found for these fatty acid esters in the food, textile
and cosmetic industry and in the manufacture of synthetic lubricants.
[0006] Another aspect that can increase the interest for this group of products is the use
of methylic and ethylic fatty acid esters as a clean alternative to diesel from the
petrochemical industry. This type of ester is known as Biodiesel (DUNNE, W. "The production
of fuels from biological substances". Int. I. Energy Res., Vol. 18, p. 71-78, 1994.;
PRYDE, E.H. "Vegetable oils as fuel alternatives". JAOCS, Vol. 61, p. 1609-1610, 1984).
Biodiesel, obtained in this way, presents excellent environmental benefits, especially
in relation to the emission of SO
2, particles and smoke.
[0007] Low molecular weight alkyl esters of fatty acids can be prepared by direct reaction
between triglycerides and the corresponding alcohol. The use of rapeseed and sunflower
oils as sources for these reactions is especially interesting because they use production
surpluses which, according to European legislation, cannot be used as food products.
The transesterification reaction can be carried out by homogeneous classical catalysis,
which is usually basic and heterogeneous or can use biocatalysts.
[0008] The catalytic transesterification of plant oils has been described since the middle
of the XIX Century. In 1852, Duffy (DUFFY, P. "On the constitution of stearine". J.
Chem. Soc., Vol. 5, p. 303, 1852) presented a procedure that used sodium methoxide
as a catalyst. However, more studies were published on this area of research around
the mid XX century. The use of different raw materials has also been studied in numerous
research projects.
[0009] In 1984, Freedman et al. (FREEDMAN, B.; PRYDE, E.H. and MOUNTS, T.L. "Variables affecting
the yields of fatty esters from transesterified vegetable oils". JAOCS, Vol. 61, p.
1638-1643, 1984), studied the alcoholysis of oils from cotton seed, peanut, soya and
sunflower with monoalkylic alcohols using basic catalysts, sodium hydroxide and methoxide,
at 60 °C. The frying oil used as raw material in Austria to obtain methylic esters
with basic catalysts (FRÖLICH, A. and RICE, B. "The preparation and properties of
biodiesel grade methyl ester from waste cooking oil". Minutes of the activity meeting
of the IEA, Vienna, p. 11-18, 1995) and more recently alcoholysis of animal tallow
has been described (MA, F.; CLEMENTS, L.D. and HANNA, M.A. "Biodiesel fuel from animal
fat. Ancillary studies on transesterification of beef tallow". Ind. Eng. Chem. Res.,
Vol. 37, p. 3768-3771, 1998).
[0010] There is also information published in the literature about the different catalytic
systems used in transesterification processes. In 1995, a process patented by Wimmer
Theodor et al. U.S. Patent n° 5434279 was described, which used basic alkaline compounds
or compounds of transition metals such as oxides, hydroxides, alcoholates, borates,
carbonates and silicates of lithium, sodium, potassium and calcium as catalysts.
[0011] In the process patented by Chien Hoang et al. in the French Patent FR2698101, other
heterogeneous catalytic systems and a variety of mixed catalysts were used. Hence,
starting with potassium carbonate-mixtures of sodium carbonate-potassium bicarbonate-sodium-potassium
carbonate and/or sodium and potassium phosphates among others, were made up.
[0012] As well as those described above, other catalytic systems were used in transesterification
processes. The patent from 1985, Volpenheim. U.S. Patent n° US4517360, describes the
use of alkaline metal salts of polyols in high concentrations in transesterification
reactions, without solvent, of complex alkyl esters using basic catalysts such as
metals, alloys and alkoxides among others. Among the polyols, monosaccharaides, disaccharides
and other sugar alcohols are important.
[0013] The kinetic study of the esterification reaction of glycerine with fatty acids in
the presence of sodium and potassium soaps was published in 1998 by Szelag et al.
(SZELAG, H. and ZWIERZYKOWSKI, W. "Esterification kinetics of glycerol with fatty
acids in the presence of sodium and potassium soaps". Fett-Lipid, Vol. 100 (7), 302-307,
1998). This shows that the rate constant of the reaction increases with increasing
concentration of the soap in the reaction medium.
[0014] The Cognis process, EP1092703 for the production of methylic fatty acids from triglycerides
is comprised of two steps. The first takes place at high pressures and temperatures
in the presence of salts of transition metals as catalyst, such as magnesium stearate.
The second step is produced after elimination of glycerine and consists in transesterification
at low pressure in the presence of sodium methoxide.
DESCRIPTION OF THE INVENTION
[0015] Procedure to transesterify triglycerides with low molecular weight monoalcohols to
obtain light alcohol esters using mixed catalysts.
[0016] The present invention describes a new semi-continuous manufacturing procedure for
light alcohol esters from fatty acids of raw, refined or used plant oils and other
triglyceride mixtures by a transesterification process. In this process, a mixed system
comprised of sodium or potassium soap obtained from the fatty acid of raw, refined
or used vegetable oils of plant or animal fat or other triglyceride mixtures and those
corresponding to sodium and potassium hydroxides are used as the catalytic system.
These esters are used as fuel in diesel engines and also as fuel for domestic use.
[0017] The present invention refers to the use of mixed catalytic systems formed of soap
and the corresponding sodium and potassium hydroxide, to direct the transesterification
of light esters of fatty acids of raw, refined or used vegetable oils, of plant oils
or animal fats and other triglyceride mixtures to obtain an ester yield above 99%,
using a semicontinuous process in which the time required to obtain this yield is
from 5 to 300 minutes although, normally, this time is between 60 and 150 minutes.
[0018] The transesterification reaction takes place according to conventional processes
in a continuous or discontinuous reactor of the stirred―tank type, to which the catalytic
system is added.
[0019] The reaction is carried out in a temperature interval of 10°C to 100°C, preferably
between 15°C and 65°C, and at atmospheric pressure. The transesterification reaction
can be carried out in one or two steps.
[0020] If the reaction is carried out in one step, the amount of alcohol used for the transesterification
varies within an interval from 70% to 250% of the stechiometric value, preferably
between 100% and 200%.
[0021] If the reaction is carried out in two steps, in the first step an amount of alcohol
between 70% and 200% of the stechiometric amount, preferably between 70% and 175%
is added to the reactor. Then, the reaction mixture is decanted to eliminate the glycerine
formed, which is transferred to the glycerine tank, and the amount of alcohol required
for this to be present in a stechiometric quantity between 100 % and 250%, preferably
between 100% and 200%, is added to the reactor. Then, the reaction mixture is transferred
to a separation system if operating in a continuous reactor or a deposit chamber for
its purification if operating in a discontinuous reactor.
[0022] In the purification steps after the transesterification reaction, the mode of operation
is continuous, independently of how the reaction system has been operated.
[0023] The catalytic system used for the transesterification reaction is a mixed system
comprised of alkaline metal hydroxides, preferably of sodium and/or potassium, and
of alkaline metal soaps, preferably of sodium and/or potassium, obtained from free
fatty acids contained in the raw materials via a process of neutralization. The neutralization
of these fatty acids is done using non aqueous solutions of alkaline metal hydroxides,
preferably of sodium and/or potassium, producing the corresponding soaps that act
as promoters or coadjuvants of the transesterification reaction.
[0024] Depending on the acidity of the starting material and the amount of soaps required
for the transesterification reaction, it will be necessary to add an amount of alkaline
metal hydroxides between 0.1 and 1.0% in weight of the reaction mass, preferably between
0.2 and 0.8%.
[0025] The reaction system formed by stirred-tank reactors is equipped with a filtered system
in order to maintain in the reaction medium the largest amount of soaps, since these
favor the progress of the transesterification reaction.
[0026] If the transesterification process is carried out in a discontinuous process, the
excess methanol or ethanol will be separated from the reaction medium by vacuum distillation.
If the transesterification reaction is conducted in continuous mode, the excess methanol
and ethanol will be separated from the reaction medium by vacuum distillation from
the deposit chamber which feeds the separation and purification processes of the biodiesel.
In both cases, the methanol or ethanol recovered will be transferred to the corresponding
methanol or ethanol storage tank.
[0027] The transesterification mixture, both if the reaction is carried out in discontinuous
mode or in continuous mode, will be transferred to a deposit chamber which, if the
reaction is conducted in continuous mode, will be equipped with a vacuum distillation
system to eliminate the excess methanol or ethanol from the reaction. This deposit
chamber, which will have between 2 and 15 times the volume of the transesterification
reactor, usually between 4 and 7 times, will continually feed the biodiesel and glycerine
separation and purification system.
[0028] The mixture from the deposit chamber will continually feed a separation system in
which two differentiated phases are obtained: the ester phase (A) and the glycerinous
phase (B).
[0029] To the ester phase (A), mainly comprised of the light alcohol ester used, the catalyst
and traces of unreacted alcohol, glycerine and soaps, will be rinsed with water and/or
a diluted solution of a strong acid, such as H
2SO
4, H
3PO
4, HCl, etc., and, then, the two phases formed will be separated. One of these phases
(A1), will mainly be comprised by the ester of the alcohol used for the transesterification.
The other aqueous phase (A2), will be submitted to a neutralization operation so that
it complies with environmental rules and regulations. These rinsing waters will be
vacuum distilled to recover any remains of methanol they may contain and transferred
to the corresponding tank of raw material.
[0030] Then, in the (A1) phase the organic compound is added so that the biodiesel formed
complies with specifications of the parameter "cold filter obturation point" (CFOP).
After this, it is dried to eliminate any traces of water or alcohol that may remain.
[0031] Next, this current with the (A1) phase, free of moisture and alcohol, is filtered
to eliminate any solid particles it may contain, either from the raw material or from
the catalytic system used.
[0032] The product obtained after the filtration step is an alkyl ester that fulfils specifications
of the European Union for its use as biodiesel.
[0033] The glycerinous phase (B) is submitted to vacuum distillation to eliminate the remains
of methanol or ethanol and is then submitted to neutralization with H
2SO
4, H
3PO
4, HCl, etc., preferably with H
3PO
4. Next, the three phases formed are separated: the liquid phase (B1) of glycerine
with a purity between 86% and 92%, the liquid phase (B2) of fatty acids (B2) and the
solid phase (B3) of the sodium or potassium salt of the acid used in neutralization
of the glycerinous phase.
APPLICATION OF THE INVENTION
[0034] The present invention is also illustrated by the following examples:
EXAMPLE 1
[0035] This example shows the influence of the activity of the catalytic system using potassium
hydroxide as the only component of this catalytic system.
[0036] The reaction was carried out in a 125 ml volume complete mixture reactor equipped
with a stirrer at 600 rpm where the reaction temperature is maintained constant at
25°C and the working pressure at atmospheric pressure.
[0037] A total of 53.40 g of the triglyceride raw material with an acidity of 10%, 14.60
g methanol and 0.2265 g potassium hydroxide (0.40% in weight, 4.04 milliequivalents)
were added to the reactor. After 60 minutes of reaction, conversion of the triglyceride
raw material was 99% and the yield in methylic esters was 95% (Yield = kg of methyl
ester produced/100 kg of triglyceride raw material added).
EXAMPLE 2
[0038] This example shows the influence of the activity of the catalytic system obtained
by neutralization with potassium hydroxide of the free fatty acids present in the
starting material that corresponds to the only component of the catalytic system.
[0039] The reaction is carried out in a 125 ml volume complete mixture reactor with a 600
rpm stirrer system where the reaction temperature is maintained constant at 25°C and
the working pressure at atmospheric pressure.
[0040] A total of 53.40 g of the triglyceride starting material with an acidity of 10% is
added to the reactor and 14.60 g of methanol. Neutralization is done stechiometrically
with 8.10 milliequivalents of potassium hydroxide, obtaining 2.6 g potassium soaps,
and the transesterification reaction begins. After 60 minutes reaction, conversion
of the triglyceride starting material was 18% and the yield of methylic esters was
15%.
EXAMPLE 3
[0041] This example shows the effect of the potassium hydroxide milliequivalents on the
composition of the catalytic system.
[0042] The following table shows the experiments carried out in the same working conditions
(type of reactor, temperature, pressure, agitation, amount of reactants and operation
time) as examples 1 and 2, changing the acidity of the triglyceride raw material to
be transesterified (between 0% and 10%).
Table I
Assay |
Acidity starting material |
Potassium soap |
KOH |
Total |
Convesion |
Yield |
(n°) |
(%) |
(g) |
(meq) |
(g) |
(meq) |
(%) |
(meq) |
(%) |
(%) |
3 |
10.0 |
2.6 |
8.10 |
0.226 |
4.04 |
0.40 |
12.14 |
99 |
95 |
4 |
5.0 |
1.3 |
4.05 |
0.226 |
4.04 |
0.40 |
8.09 |
97 |
93 |
5 |
1.0 |
0.26 |
0.80 |
0.460 |
8.10 |
0.81 |
9.00 |
100 |
96 |
6 |
1.2 |
0.32 |
0.99 |
0.138 |
2.46 |
0.24 |
3.45 |
75 |
72 |
7 |
0.7 |
0.23 |
0.71 |
0.223 |
3.97 |
0.39 |
4.68 |
96 |
92 |
8 |
0.4 |
0.14 |
0.43 |
0.314 |
5.60 |
0.56 |
6.03 |
100 |
96 |
9 |
1.2 |
0.32 |
0.99 |
0.0 |
0.00 |
0.00 |
0.99 |
7 |
4 |
10 |
0.0 |
0.0 |
0.00 |
0.138 |
2.46 |
0.24 |
2.46 |
68 |
65 |
11 |
0.4 |
0.14 |
0.43 |
0.0 |
0.00 |
0.00 |
0.43 |
4 |
3 |
12 |
0.0 |
0.0 |
0.00 |
0.223 |
3.97 |
0.39 |
3.97 |
95 |
91 |
13 |
10.0 |
2.6 |
8.10 |
0.0 |
0.00 |
0.00 |
8.10 |
18 |
15 |
[0043] As can be observed in the table, use of the mixed catalytic system gives a higher
yield of methylic esters in the reaction, compared to that obtained with potassium
hydroxide as the only component of the catalytic system, at the same milliequivalents
of potassium hydroxide used.
EXAMPLE 4
[0044] This example shows the influence of the reaction temperature.
[0045] Assay number 3, shown in Table I, was repeated with the same catalytic system and
working conditions except for the reaction temperature, which was maintained constant
at 65°C. After 60 minutes of reaction, conversion of the triglyceride starting material
was 100%, with a yield of methylic esters of 91%.
EXAMPLE 5
[0046] This example shows the influence of reaction time.
[0047] Assay number 3, shown in Table I, was repeated with the same catalytic system and
working conditions with the exception of reaction time, which was 20 minutes. Conversion
of the triglyceride starting material was 90%, with a yield of methylic esters of
86%.
EXAMPLE 6
[0048] This example shows the influence of reaction time.
[0049] Assay number 3, shown in Table I, was repeated with the same catalytic system and
working conditions except for reaction time. After 120 minutes of reaction, conversion
of the triglyceride starting material was 100%, with a yield of methylic esters of
96%.
EXAMPLE 7
[0050] This example shows the influence of stirring rate.
[0051] Assay number 3, shown in Table I, was repeated with the same catalytic system and
working conditions except for stirring rate, which was 100 rpm. After 60 minutes,
conversion of the triglyceride starting material was 40%, with a yield of methylic
esters of 35%.
EXAMPLE 8
[0052] This example shows the influence of the type of cation present in the hydroxide that
will form part of the catalytic system.
[0053] Assay number 3, shown in Table I, was repeated with the same catalytic system and
working conditions except for potassium hydroxide, which was replaced by sodium hydroxide.
After 60 minutes, conversion of the triglyceride starting material was 99%, with a
yield of methylic esters of 93%.
EXAMPLE 9
[0054] This example shows the mode of operation of the transesterification process.
[0055] In a 125 ml volume complete mixture tank reactor, equipped with a stirring system,
53.40 g of triglyceride starting material, with an acidity of 0.4%, and 7.25 g of
methanol were introduced. The reaction temperature was maintained constant at 25°C,
at atmospheric pressure and a stirring rate of 600 rpm. Neutralization was done stechiometrically
with 0.71 milliequivalents of potassium hydroxide. Then, 0.32 g potassium hydroxide
were added to the reaction mixture to complete the mixed catalytic system.
[0056] After 20 minutes, the glycerine formed in the transesterification is separated, obtaining
80% conversion of the triglyceride starting material. Next, 2.90 g methanol are added
to the reaction system and after 20 minutes 99% conversion of the triglyceride starting
material was obtained, with a yield of methylic esters of 96%.
EXAMPLE 10
[0057] This example shows the influence of the molecular weight of the alcohol used in the
transesterification reaction.
[0058] Assay number 3, shown in Table I, is repeated with the same catalytic system and
working conditions except that methylic alcohol was replaced by ethylic alcohol in
the transesterification process. After 60 minutes, conversion of the triglyceride
starting material was 38%, with a yield of methylic esters of 35%.
EXAMPLE 11
[0059] This example shows the mode of operation.
[0060] The reaction is carried out in a 2000 ml complete mix reactor equipped with an 800
rpm stirring system where the reaction temperature is kept constant at 25°C and the
working pressure at atmospheric pressure.
[0061] A total of 842.6 g of the triglyceride starting material for transesterification
with an acidity of 3% is added to the reactor. Next, a solution containing 5.0 g potassium
hydroxide in 88.7 g methanol is added. At this moment, the free fatty acids are neutralized
forming the corresponding potassium soap. After this step, 5.3 g of dissolved potassium
hydroxide are added dissolved in 88.7 g methanol. The mixture is stirred, triggering
the transesterification reaction. After 60 minutes., the reaction is completed and
the two liquid phases that have formed are separated.
[0062] The ester phase (A), contains 810.5 g of fatty acid methylic ester, 45.1 g methanol,
3.8 g triglycerides, 2.9 g fatty acids and 0.3 g potassium soap. The glycerinous phase
(B), contains 85.0 g glycerine, 44.8 g methanol, 39.7 g potassium soap, 5.2 g potassium
hydroxide and 0.2 g methylic esters.
[0063] The ester phase is rinsed using 409.1 g water. The two immiscible phases formed are
separated, obtaining the following composition for each of them. The ester phase (A1)
contains 808.7 g methylic esters, 3.8g triglycerides and 2.9 g fatty acids. The aqueous
phase (A2) contains 409.1 g water, 45.1 g methanol, 1.6 g methyl esters and 0.3 g
potassium soaps. The aqueous phase (A2) is then submitted to distillation at 25°C
and a pressure of 16 mmHg, collecting the 45.1 g methanol it contained.
[0064] The glycerinous phase (B), is also submitted to distillation at 25°C and a pressure
of 16 mmHg, collecting the 44.8 g methanol it contained. Next, a solution of 21.4
g ortho-phosphoric acid in 9.1 g water is added to the glycerinous phase (B) devoid
of methanol. In this process, three different phases are formed: two liquid phases
and one precipitated solid phase. These three phases are separated obtaining the following
composition for each of them. The (B1) phase contains 85.0 g glycerine, 9.1 g water
and 0.2 g methylic esters. Phase (B2) is composed of 34.9 g fatty acids and phase
(B3) is composed of 27.6 g of a precipitate comprised of potassium phosphate salts.
1. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain
light alcohol esters using mixed catalysts characterized in that the triglycerides come from raw, refined or used vegetable oils, plant oils or animal
fats, and mixtures thereof.
2. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain
light alcohol esters using mixed catalysts, according to the previous claim, characterized in that the monoalcohols are preferably methanol and ethanol.
3. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain
light alcohol esters using mixed catalysts, according to the previous claim, characterized in that the mixed catalytic system is comprised of alkaline metal hydroxides, preferably
sodium and potassium, and of soaps obtained from free fatty acids contained in the
starting materials by a process of neutralization.
4. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain
light alcohol esters using mixed catalysts, according to claim 3, characterized in that the neutralization of the acidity of the raw materials is performed by the alkaline
hydroxides forming the corresponding salts of carboxylic acids employed in the catalytic
system.
5. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain
light alcohol esters using mixed catalysts, according to claims 3 and 4, characterized in that the amount of alkaline hydroxides used, ranges between 0.1 and 1% of the reaction
mass.
6. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain
light alcohol esters using mixed catalysts, according to previous claims, characterized in that it uses continuous or discontinuous reactors, of the stirred-tank type, equipped
with a filtration system at the exit of the reaction system.
7. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain
light alcohol esters using mixed catalysts, according to previous claims, characterized in that the transesterification reaction is carried out at a temperature between 10° and
100°C and in a time between 5 and 300 minutes.
8. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain
light alcohol esters using mixed catalysts, according to previous claims, characterized in that the transesterification reaction is carried out in one step introducing in the reactor
an amount of alcohol ranging from 70 to 250% of the stechiometric amount.
9. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain
light alcohol esters using mixed catalysts, according to claims 1 to 7,
characterized in that the transesterification reaction is carried out in two steps:
1. An amount of alcohol between 70 and 200% of the stechiometric amount is introduced
in the reactor.
2. The glycerine formed is separated from the reaction mixture and the required amount
of alcohol is added to the reactor for this to encounter an amount between 100 and
250% of the stechiometric value.
10. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain
light alcohol esters using mixed catalysts, according to previous claims, characterized in that the transesterification reaction is carried out in a discontinuous process in which
the excess methanol or ethanol is separated from the reaction medium by a vacuum distillation
operation.
11. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain
light alcohol esters using mixed catalysts, according to claims 1 to 9, characterized in that the transesterification reaction is carried out in a continuous process in which
the excess methanol or ethanol is separated from the reaction medium by vacuum distillation
from the deposit chamber.
12. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain
light alcohol esters using mixed catalysts, according to previous claims, characterized in that the reaction mixture is transferred to a deposit chamber to be subsequently purified
and obtain the light alcohol esters (biodiesel) and by-products, which are made after
this time in continuous mode.
13. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain
light alcohol esters using mixed catalysts, according to the previous claim, characterized in that the mixture from the deposit chamber continuously feeds a separation system from
which two phases are obtained: (A) the ester phase, mainly comprised of the ester,
alcohols and soaps, and (B) the glycerine phase mainly comprised of glycerine, alcohol
and soaps.
14. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain
light alcohol esters using mixed catalysts, according to the previous claim,
characterized in that the ester phase is rinsed with water or with a diluted solution of strong acid, being
separated into:
(A1). A phase comprised of the alcohol ester used for transesterification, to which
an organic compound is added, to proceed to a drying operation followed by a filtration
process obtaining an alkyl ester suitable for use as a combustion agent, fuel or solvent.
(A2). An aqueous phase submitted to a neutralization operation followed by vacuum
distillation.
15. Process to transesterify triglycerides with low molecular weight monoalcohols to obtain
light alcohol esters using mixed catalysts, according to claim 13,
characterized in that the glycerine phase (B) is submitted to a vacuum distillation operation followed
by neutralization with strong acid, preferably
ortho-phosphoric acid giving rise to three by-products:
(B1). Liquid phase that contains glycerine
(B2). Liquid phase that contains fatty acids
(B3). Solid phase that contains a sodium or potassium salt of the acid used in the
neutralization.
16. Use of the esters obtained with the claimed transesterification process as combustion
agents, fuels and solvents.